1. Field of the Invention
The present invention concerns a thin film read transducer utilizing the magnet resistance (MR effect) and, more in particular, it relates to a magnetoresistive read transducer suitable to recording/reproduction of information signals in a magnetic recording device.
2. Related Art Statement
Along with the improvement of recording density, it has become necessary to increase the density of a sense current in a magnetoresistive read transducer (hereinafter referred to simply as "MR effect type head") in order to ensure a high head output.
It has been known that remarkable burning out or migration degradation is caused by temperature rise in a magnetoresistive element as the current density increases to more than 2.times.10.sup.7 (A/cm.sup.2) or 3.times.10.sup.7 A/cm.sup.2) compared with a current density of about 1.times.10.sup.7 (A/cm.sup.2).
As shown in FIG. 5, a MR effect type head 51 comprises a central active region for sensing a magnetic field of a medium (also referred to as a magnetoresistive sensing element portion), and tail regions 51B, 51C (also referred to as a longitudinal bias layer) for supplying a longitudinal bias or a sense current to the central active region 51A, in which contact resistance is inevitably caused upon electric connection of them with each other.
Since the density of the sense current is relatively small, control for the contact resistance has not been sufficient. On the other hand, when a conduction test has been actually conducted in the MR effect type head 51 with an increased density of the sense current, it has been confirmed that the resistance of the head increases with lapse of time and an increasing phenomenon of a failed head (change of resistance value by 10% from an initial value before conduction test) has been observed.
For the temperature rise in the head portion of MR effect type heads has been pointed out, although not disclosing the resistance value, in Japanese Patent Laid-Open Hei 7-320236 and Hei 4-271001.
Further, when an accelerated conduction test has been conducted actually, it has been confirmed that abnormality occurs not only in the element portion of the MR effect type head 51 but also in the shielding portion, for example, as elimination or depletion of the layer.
Namely, in the existent MR effect type head 51 described above, temperature rise in the MR element portion results in temperature rise in the shielding portion at the periphery thereof, which is considered to cause the abnormal operation. However, no particular consideration has been taken for the countermeasure (efficient heat dissipation or the like).
Generally, as the density of the magnetic recording increases, the recording wavelength and the width of recording tracks are decreased and the reproducing output of a magnetic head tends to be lowered correspondingly. Various methods may be considered for increasing the reproducing output of the MR effect type head. For instance, a most reliable method is to increase the value of the sense current supplied to the MR element portion. If the sense current increases, the output of the MR effect type head increases substantially in proportion therewith.
On the contrary, since Joule's heat formed in the MR element portion is also increased, the temperature in the MR element portion also rises remarkably. It has generally been known that if the temperature of the MR element portion is excessively high, the output is rather lowered even when the value of the sense current increased exceeding a certain level. In view of the above, it is important to suppress the temperature rise as low as possible even if the value of the sense current is increased.
At the same time, the electric conduction life of the MR effect type head has to be taken into a consideration as a problem with regard to the temperature rise. The electric conduction life of the MR effect type head is determined mainly by the density of the sense current and the element temperature, which is highly sensitive to the temperature and changed exponentially, and lowered greatly by the temperature rise.